1. Field of the Invention
The present invention relates to a power supply unit and an image forming apparatus.
2. Description of the Related Art
Many electric apparatuses have a power-saving mode for saving electricity. For example, generally, an image forming apparatus has three modes: power off mode, standby mode; and sleep mode. In the power off mode, the main power switch is turned off and no power is supplied to the apparatus. In the standby mode, the main power switch is on, whereby an alternating current (AC) power is supplied to the apparatus and an image can be formed immediately by driving mechanical loads with a motor clutch and the like by generating a direct current (DC) power of 5 V (volt), 24 V, and the like used therein.
The apparatus enters the sleep mode when the apparatus is not operated for a certain period of time, or when an instruction is received from the user. In the sleep mode, power is supplied only to certain specific units in the apparatus and power supply to other units in the apparatus is cutoff. Thus, the power consumption is reduced. The apparatus switches to the standby mode from the sleep mode when a return sensor output and a host interface (I/F) is connected to the units supplied with power and a change in an output condition of the sensor output or a signal condition of the host I/F is detected. Specifically, the apparatus under the sleep mode switches to the standby mode and starts printing when the user instructs the apparatus copy or document reading, the apparatus receives an instruction for printing from an external host such as a local area network (LAN) and a universal serial bus (USB), and when the apparatus receives a fax.
An outline of a configuration of a conventional image forming apparatus that performs such an operation is explained with reference to a block diagram in FIG. 7. As shown in FIG. 7, the conventional image forming apparatus includes an AC plug 1001, an AC switch 1002, a power supply unit 1004, a mechanical controlling unit 1005, a mechanical load controlling unit 1006, a system controlling unit 1007, an image reading unit 1008, an image writing unit 1009, a host 1010, and a return sensor 1011.
When the AC plug 1001 is connected to an AC outlet and the AC switch 1002 is closed (turned on), an AC power is supplied to the power supply unit 1004. The power supply unit 1004 generates DC powers of 24 V, 5 V, and the like. The DC power is supplied to the mechanical controlling unit 1005, the system controlling unit 1007, and the like via a switch SW1 for 24 V and a switch SW2 for 5 V.
The mechanical load controlling unit 1006 includes a central processing unit (CPU) and an input-output (IO) control driver (not shown). The CPU starts upon power supply and drives mechanical loads in a predetermined image-forming sequence.
The image reading unit 1008 includes a lamp and a charge-coupled device (CCD) (not shown) and reads an image of an original by irradiating the original on a platen with light and receiving the reflected light with the CCD.
The system controlling unit 1007 operates in synchronization with the mechanical controlling unit 1005 when the apparatus performs copying. The system controlling unit 1007 reads image data from the image reading unit 1008, and after performing various imaging processing, sends the image data to the image writing unit 1009.
The image writing unit 1009 controls on and off of laser diodes in accordance with the image data received from the system controlling unit 1007 to irradiate a photoreceptor drum with a laser beam for forming an electrostatic latent image thereon. The electrostatic latent image formed on the drum is developed with a toner and image forming is completed by copying the toner image on to paper. The process of copying an image formed on the drum on to paper is not a subject matter of the invention. Thus, the detailed explanation of the process is omitted.
The system controlling unit 1007 is connected to the host 1010 through an interface such as a LAN and a USB. When printing, the system controlling unit 1007 performs imaging processes including zoom in/out, and arranging layouts of the image data received from the host 1010 and sends the data to the image writing unit 1009. The image writing unit 1009 performs the similar processes to form the image the user requires.
The power supply unit 1004 includes one switch for each of the outputs 24 V and 5 V. Those switches can be turned on and off in accordance with a PON_ENG signal output from the system controlling unit 1007. The system controlling unit 1007 is supplied with a DC power 5 VE before switching while the mechanical controlling unit 1005 that consumes more electricity is supplied with DC power of 5 V and 24 V after switching.
The return sensor 1011 including a power switch on a control panel, an original set detecting sensor, and a pressure plate opening/closing detecting sensor (not shown) is connected to the system controlling unit 1007. When the apparatus is under the sleep mode, the system controlling unit 1007 constantly monitors an output from the return sensor 1011 to decide whether the user has operated the apparatus. Similarly, the system controlling unit 1007 constantly monitors whether an instruction to print is input from the host 1010, and whether a fax is received.
The system controlling unit 1007 sets the level of the PON_ENG to a logical high level when a returning factor from the return sensor 1011 or the host 1010 is detected. The operation is caused by an input of a certain signal from the return sensor 1011 or the host 1010. The power supply unit 1004 is switched on when it receives the PON_ENG from the system controlling unit 1007. Consequently, power of 5 V and 24 V is supplied to the mechanical controlling unit 1005 from the power supply unit 1004 and the operational state of the apparatus switches (returns) to a mode capable of forming an image.
On the other hand, the system controlling unit 1007 switches off the power supply unit 1004 by setting the level of the PON_ENG to a logical low level when the unit detects that the apparatus has not been operated for a certain period of time or the user has instructed the apparatus to enter the sleep mode using the control keys. The apparatus can switch to the sleep mode by negating the PON_ENG to cut off the power of 24 V and 5 V supplied to the mechanical controlling unit 1005.
FIG. 8 is a timing chart of these operations. When the AC switch is turned on (“power sw on”), an AC power is supplied to the power supply unit 1004 and an oscillation circuit (not shown) starts to oscillate (“oscillation circuit output”). A DC voltage generator generates a 5 VE (“5 VE”) as a secondary voltage by transforming and rectifying the output of the oscillation circuit (“DC voltage output”). When the 5 VE is supplied to the system controlling unit 1007, a CPU in the system controlling unit 1007 starts and the PON_ENG (“PON_ENG”) is asserted. Upon assertion of the PON_ENG, the SW1 and the SW2 in the power supply unit 1004 are switched on and the 5 V and 24 V outputs (“power for mechanical control”) are supplied to the mechanical controlling unit 1005. Consequently, the system starts and the apparatus enters a standby mode (“standby”).
When a timer in the system controlling unit 1007 detects that the apparatus has not been operated for a certain period of time (“timer up”), the PON_ENG (“PON_ENG”) is negated to cut off the 5 V and 24 V outputs and the apparatus enters the sleep mode (“sleep mode”). Under the sleep mode, the CPU in the system controlling unit 1007 constantly monitors the return sensor 1011 and when it is detected that, for example, the user has operated the image forming apparatus, the PON_ENG (“PON_ENG”) is asserted again to turn on the 5 V and 24 V outputs. Consequently, the image forming apparatus is started, that is, the apparatus again enters the standby mode.
With the above-described configuration and functions, the power consumption of the conventional image forming apparatus is reduced by automatically causing the apparatus to enter the sleep mode when the apparatus has not been operated for a certain period of time, and automatically return when the apparatus detects a signal for returning such as a return sensor output and an access signal from the host 1010.
Japanese Patent Application Laid-open No. 2001-69687, for example, teaches use of solar batteries as the power source in the sleep mode has been proposed to further reduce the power consumption when the apparatus is under the sleep mode. As explained, for the apparatus to automatically return to the standby mode, the return sensor 1011 and the system controlling unit 1007 must partly be supplied with power when the apparatus is under the sleep mode. A technique disclosed in Japanese Patent Application Laid-open No. 2001-69687 further reduces the power consumption by using a solar battery to supply power to part of the return sensor 1011 and the system controlling unit 1007 in an example arrangement illustrated in FIG. 7.
An example of a configuration of a conventional power supply unit using a solar battery as a power source is shown in FIG. 9. When the apparatus is in the normal operating mode, a charge circuit 1110 supplies a voltage output 2 from a DC power supply circuit 1105 to a monitoring circuit 1104 and a detecting circuit 1103 that detects a returning factor, and charges a storage battery 1111. When the apparatus is in the low-power consumption mode, the storage battery 1111 supplies the voltage output 2 to the monitoring circuit 1104 and the detecting circuit 1103. In the low-power consumption mode, the charge circuit 1110 charges the storage battery 1111 only when light is falling on a solar battery 1113. Thus, the power supply unit can cut off the voltage output 2 when the storage battery 1111 discharges for a certain amount and a power threshold detecting circuit 1112 detects that the voltage has fallen below a certain threshold.
When power switching circuits 1107 and 1108 are closed, an AC power is supplied to the DC power supply circuit 1105. The DC power supply circuit 1105 supplies a voltage output 1 to a controlling circuit 1106. The controlling circuit 1106 controls the apparatus in the normal operation mode.
When switching to the low-power consumption mode, the controlling circuit 1106 sends a signal to the DC power supply circuit 1105 to stop the output. Upon receiving the signal, the DC power supply circuit 1105 stops the voltage output 1 and the controlling circuit 1106 stops controlling the apparatus. In the low-power consumption mode, the storage battery 1111 supplies the voltage output 2 to the monitoring circuit 1104 and the detecting circuit 1103.
Under the low-power consumption mode, when the detecting circuit 1103 detects any returning factor, a signal is sent to the monitoring circuit 1104. The DC power supply circuit 1105 supplies the voltage output 1 to the controlling circuit 1106 and the controlling circuit 1106 switches the apparatus to the normal operation mode from the low-power consumption mode.
In the example of this conventional power supply unit, when the power threshold detecting circuit 1112 detects that the voltage of the storage battery 1111 has fallen below a certain threshold, the power from the storage battery 1111 to the detecting circuit 1103 and the monitoring circuit 1104 is cut off and the apparatus is turned off. Thus, after the power is off, the sleep mode, in which the apparatus can return to the normal operation mode upon receiving any returning factor, cannot be maintained.
The power shortage of a power source charged by the solar battery in the low-power consumption mode may be compensated by activating the main power supply to charge the storage battery. However, to do so, the load increases and as a result, the power consumption increases.
To solve these problems, Japanese Patent Application Laid-open No. 2003-29579, for example, discloses an image forming apparatus including a main power supply, a solar battery, a secondary battery charged by the main power supply or the solar battery, and a controlling unit that stops the operation of the main power supply and supplies power to units in the apparatus using the secondary battery in the low-power consumption mode. This apparatus includes a power supply threshold detecting unit that monitors the level of the secondary battery. In the low-power consumption mode, when the power supply threshold detecting unit detects that the voltage of the secondary battery has fallen below a certain threshold, the controlling unit blocks paths for supplying power to units in the apparatus. Thus, load on the secondary battery is reduced and a long low-power consumption mode using the secondary battery as the power source can be maintained.
As another way of generating power other than solar batteries, Japanese Patent Application Laid-open No. 2005-354888, for example, discloses electric wave power generation that generates power from electric waves in a living space.
The techniques disclosed in Japanese Patent Application Laid-open No. 2001-69687 and Japanese Patent Application Laid-open No. 2003-29579 use solar batteries. Therefore, power cannot be generated unless the apparatus receives light. The storage battery is used to supply power to the apparatus under the sleep mode in an environment without light in Japanese Patent Application Laid-open No. 2001-69687 and Japanese Patent Application Laid-open No. 2003-29579. However, as the storage battery discharges, the voltage thereof decreases and the voltage may drop to a level that power needed to maintain the sleep mode cannot be supplied. The technique disclosed in Japanese Patent Application Laid-open No. 2003-29579 includes a power supply threshold detecting unit to block paths for supplying power to units in the apparatus when the power supply threshold detecting unit detects that voltage of the storage battery has fallen below a certain threshold. However, in this case, the power of the apparatus is turned off and the sleep mode, in which the apparatus can return to the normal operation mode upon receiving any returning factor, cannot be maintained.
The object of the technique disclosed in Japanese Patent Application Laid-open No. 2005-354888 is electric wave power generation. The technique is not related to using the electric wave power generation in a complementary style with a commercial AC power supply to reduce consumption of the commercial AC power supply in the low-power consumption mode.